Creating an electrical and mechanical connection between two dissimilar surfaces is important for grounding and creating mechanically robust vehicles.
For example, lightning protection of composite structures, which are extensively used on new aircrafts and other vehicles, is complex due to the inherent electrical resistance of carbon fibers and epoxy, as well as the multi-layer construction. The intrinsic high conductivity of metallic fasteners means that lightning currents may create detrimental ignition sources by flowing current through a metallic fastener to another point, thereby creating arcing between fastener and the composite structure.
Currently, creating an electrical and mechanical connection between two dissimilar surfaces can be done in various ways.
A metallic solder can be used to create a connection. However, this requires high temperatures that both surfaces may not be able to tolerate. For example, carbon fiber composites cannot be exposed to over 254° C., which is below the melting temperature of many solders.
A conductive adhesive may be employed. However, conductive adhesives are more resistive than a metallic bond. This can result in a charge differential between the two surfaces and electrostatic discharge. Also, conductive adhesives generally do not provide a high degree of mechanical strength.
A soft metallic insert may be incorporated between the two surfaces, followed by bolting the surfaces together. However, this creates a weak point between two surfaces.
Other methods to connect two surfaces such as welding are not possible if one of the surfaces is non-metallic.
Gallium-based peritectics have been proposed as dental filling materials in Smith et al., “Alloys of gallium with powdered metals as possible replacement for dental amalgam” J. Am. Dent. Assoc. 1956, 53, 315-324; Smith et al., “Some physical properties of gallium-copper-tin alloys” J. Am. Dent. Assoc. 1956, 53, 677-685; Dunne et al., “A 3-year longitudinal, controlled clinical study of a gallium-based restorative material” British Dental Journal 2005, 198, 355-359, and U.S. Pat. No. 2,864,695 (Dec. 16, 1958). However, these publications do not describe the use of these peritectics to bond two dissimilar surfaces. They are just intended to fill holes in dental procedures.
Eutectic bonding, also referred to as eutectic soldering, is a wafer bonding technique with an intermediate metal layer that can produce a eutectic system. Eutectic bonding is used to bond semiconductor components and wafers. This bonding occurs at elevated temperatures (>100° C.) and does not use a Ga-based liquid metal.
What is needed is a metallic gap filler, which creates an electrical and mechanical connection between two dissimilar surfaces where one of the surfaces is non-metallic. Methods of creating these metallic gap fillers, compositions useful for filling gaps between surfaces, and resulting systems are desired commercially.